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Another problem is the little adapter, which is steel and therefore subject to corrosion. Craig Sawyers reports, “Mine
was rusted solid inside, and so totally inoperative.” Steve Haley says, “The short metallic slightly conical connector
was completely plugged with corrosion. The hose into the tank crumbled in my hands...and the metal brackets were
rusted and in pieces.”
Yet another concern: The end of the rubber hose inside the atmospheric catchment tank obviously needs to be open,
both to allow coolant out and to suck coolant back in. In some cases, the hose blows coolant just fine, but when
sucking the tip of the hose gets sucked onto the bottom of the tank (or even onto the side, if someone is really unlucky).
It then can’t pull in any more fluid even though surrounded by fluid, so the system pulls in some air from somewhere
else instead -- or starts sucking radiator hoses flat, which is also trouble.
The fix is easy: pull the hose out of the atmospheric catchment tank, and redesign the tip of the hose so it can’t possibly
get sucked onto a surface. One idea is to punch a 1/4” hole through the hose crossways about a half inch from the tip.
This will prevent the hose from sucking up the bottom 1/2” of the fluid in the atmospheric catchment tank, but typically
you’d rather not suck up the dregs anyway.
When fooling with the coolant recovery hose, remember that the hole where it enters the top of the atmospheric
catchment tank is supposed to be airtight so that fluid won’t overflow out that point if the tank gets full.
AIR PURGE SYSTEM: When coolant is added to a cooling system, there is always some air diffused in the liquid.
Over time, this air will come out of solution and rise to the top of the liquid, forming air pockets. To avoid creating hot
spots (since the air won’t cool the metal adjacent to it as well as the liquid would), the idea is to design the system so
the air will collect in a spot where it won’t do any harm so the owner can deal with it at his leisure.
In old pickup trucks, the top of the radiator was the highest point in the cooling system. As a result, any air in the
system would tend to collect right under the cap; all the owner had to do was top it up on occasion and the rest of the
circuit would remain air-free. Unfortunately, when Jaguar designed the XJ-S, the hoodline of a 1950 Ford pickup was
not considered acceptable; not only would the top of the radiator have to be so low that it would not be the highest point
in the system, but it wouldn’t have a cap on it either. Hence, more elaborate measures were necessary to continuously
purge air out of the system.
These measures changed with the introduction of a second radiator cap on the bypass pipe with the introduction of the
H.E. Mike Morrin says, “The Pre-H.E. XJ-S has only the cap on the header tank. The level of the cap is marginally
below the radiator vent valve (with the car on level ground).” There was a small tube from the top right corner of the
radiator over into the top of the header tank on the left wheel well. The bottom of the header tank was connected into
the return line from the heater line, which is essentially the suction side of the pump. The pump operation would
therefore draw a flow from the top of the radiator into the header tank. Within the header tank, the air would tend to
rise out and collect under the radiator cap while liquid coolant went out the bottom back into the circuit. The owner
simply tops up the system every now and then to keep air out.
With the H.E., it was decided to add a second fill cap on the bypass pipe. This formed another high spot where air
would collect. So, the air purge tubing from the top of the radiator to the header tank was modified to include a hose
connection for a line from a tap just under this second cap. Unfortunately, this complicated matters; the bypass pipe is
connected to the suction side of the pump, so it’s at low pressure. So, the coolant and air is likely to flow into the fill
connection rather than out toward the header tank. To make the air purge system work right, connections to the header
tank were revised. Rather than simply relying upon the suction side of the pump to draw coolant, an ejector was
incorporated into the air purge tubing to provide even more suction so as to pull air out of the cap fitting on the bypass
pipe. To operate this ejector, a hose was provided from the left side thermostat housing (high pressure) and there’s a
special connection on the bypass pipe directly into the suction side of the pump to get the lowest pressure possible. The
high flow resulting is routed through the ejector to provide as much suction as possible. The connection to the heater
return line was eliminated; the heater line merely passes underneath the header tank on its way to the radiator outlet.
Correction: The ©1982 Supplement, page 26-1, Fig. 2 showing the cooling system schematically shows the ejector
(item 18) incorrectly; the line from the radiator and the line from the left side thermostat housing are interchanged.